1. Field of the Invention
The present invention relates to instructional devices and, more particularly, is directed to apparatus for demonstrating the operation of an aircraft.
2. Description of the Invention Background
Today, prospective airplane pilots must undertake a rather extensive study of the principles of flight and log a number of hours in the air under the watchful eye of a flight instructor before they can be licensed to fly airplanes. Such study involves acquiring a basic understanding of the aerodynamic theory relating to wings and airfoils.
Aircraft wings are constructed so as to take advantage of certain physical principles. Perhaps the single most important wing characteristic that determines its continued flight is its "angle of attack". A wing's angle of attack is the angle between the "relative wind" and the wing's "chord line". The relative wind is the direction of airflow with respect to an aircraft's wings as it moves through the air. The aircraft's "instantaneous flight path" determines the direction of the relative wind. A wing's chord line is a reference line that extends from the wing's leading edge to its trailing edge. By changing an aircraft's angle of attack, the pilot can control the lift, airspeed and drag experienced by the aircraft. Even the total load supported in flight by the wing may be modified by variations in the angle of attack and, when coordinated with power changes and manipulation of auxiliary devices such as flaps, slats, etc., is the essence of airplane control.
Tests conducted in wind tunnels have shown that, as air flows along the surface of a wing at different angles of attack, areas of negative pressure and areas of positive pressure are created along the wing's surfaces. As the angle of attack changes, so does the various pressure distribution characteristics. Wing designers total these positive and negative forces created by these areas of pressure to obtain a resultant force on the wing for a particular angle of attack. The point of application of this resultant force is known as the "center of pressure". For any given angle of attack, the center of pressure is the point where the resultant force crosses the wing's chord line. Thus, if the designer could locate the wing so that its center of pressure was always at the aircraft's center of gravity (i.e., a point on the aircraft at which all of its weight is concentrated such that the aircraft could be balanced thereon), the aircraft would always be balanced. This is not possible, however, because the location of the center of pressure changes with the wing's angle of attack.
In an airplane's normal range of flight attitudes, the center of pressure moves forward as the angle of attack increases. As the angle of attack decreases, the center of pressure moves rearwardly. Because the center of gravity for an unloaded aircraft is fixed, the forward movement of the center of pressure as a result of an increase in the angle of attack tends to raise the nose of the aircraft and causes the angle of attack to increase even more. Conversely, if the angle of attack is decreased, the center of pressure moves rearwardly and tends to decrease the angle a greater amount. As such, it is evident that an ordinary aircraft wing is inherently unstable and that an auxiliary device, such as the horizontal tail surface must be added to enable the aircraft to balance longitudinally.
Thus, the balance of an aircraft depends on the relative position of the aircraft's center of gravity and the center of pressure on the aircraft's wings. Moreover, aircraft loading and weight distribution affect the aircraft's center of gravity and, thus, affect the balance of the aircraft. Accordingly, a pilot must have a good understanding of the relationship between the angle of attack, the center of pressure and the center of gravity in order to keep the aircraft stable.
Pilots must also have an understanding of how the aircraft's angle of attack and the aircraft's velocity relate to the lift forces created on the wings of the aircraft. In particular, if an aircraft is traveling at a constant velocity and the aircraft's angle of attack is increased, the aircraft will climb. Similarly, if the angle of attack is maintained constant and the aircraft's velocity is increased, the aircraft will climb. Therefore, to maintain the aircraft in a state of equilibrium, as velocity is increased, the lift forces must be decreased by decreasing the angle of attack. Similarly, if the aircraft's velocity is decreased, the angle of attack must be increased to keep the aircraft flying level.
Aircraft designers calculate recommended air speeds for every angle of attack, based on a standard set of parameters regarding aircraft weight and loading distribution and various atmospheric conditions such as air temperature and humidity. The designers also calculate the maximum angle of attack the aircraft can assume, based on those parameters, without ceasing to fly. These recommended flying parameters are set forth in materials that the pilot typically takes aboard with him while flying the aircraft. Of course, on days wherein the atmospheric conditions vary from the atmospheric conditions upon which such calculations were based, the pilot must make the necessary adjustments, often instantaneously, to keep the aircraft flying. Thus, it becomes even more evident why a pilot must have a thorough understanding of how an aircraft's angle of attack affects its ability to fly.
Another reason why pilots must have a thorough understanding of the effects brought about by changes in an aircraft's angle of attack, is centered around a pilot's inability to perceive such changes. For example, due to such imperceivable changes, a pilot could be flying at an angle of attack that is dangerously close to the aircraft's stall angle.
In an effort to provide pilots with an instantaneous indication of the aircraft's angle of attack, various automatic angle of attack indicators have been developed and are being used on some aircraft; however, angle of attack indicators are not, to date, standard equipment on every aircraft. Some individuals have postulated that the reason for not having angle of attack indicators on every aircraft centers around pilot ignorance. That is, the current methods and models used to educate pilots fail to provide pilots with an adequate appreciation and understanding of the relationships between an aircraft's angle of attack, loading and load distribution characteristics and center of pressure.
For example, U.S. Pat. No. 1,876,418 to Holst, issued Sep. 6, 1932; U.S. Pat. No. 2,331,304 to Carmody, issued Oct. 12, 1943; U.S. Pat. No. 2,495,709 to Drown et al., issued Jan. 31, 1950; and U.S. Pat. No. 2,584,113 to Butler, issued Feb. 5, 1952 all disclose educational apparatuses and models for simulating the operation of an aircraft. However, those apparatuses are expensive to manufacture, cumbersome to transport and operate and none of them serve to demonstrate the interrelationships between, among other things, an aircraft's angle of attack, instantaneous flight path, center of pressure, load distribution, and a pilot's viewing attitude.
Thus, there is a need for an educational apparatus that is relatively inexpensive to manufacture and easy to use that serves to demonstrate the interrelationships between an aircraft's angle of attack, instantaneous flight path, center of pressure, load distribution, and a pilot's viewing attitude.